3D-printed ‘smart’ devices monitor own use without electricity

10 Oct 2018

Professional Engineering

The University of Washington team 3D printed an e-NABLE arm with a prototype of their bidirectional sensor (blue and white) that monitors the hand opening and closing by determining the angle of the wrist (Credit: Mark Stone/ University of Washington)

3D-printed devices have tracked their own use and wirelessly shared the information without using batteries or electronics, in a potentially important breakthrough for biomedical devices.

Additive manufacturing is a “perfect” technology for making assistive technology such as prosthetic limbs or ‘smart’ pill dispensers because it is cheap and easily customisable, said a team of engineers at the University of Washington in the US.

Printed plastic parts do not contain electronics, however, meaning health agencies cannot monitor how patients are using them.

“We're interested in making accessible assistive technology with 3-D printing, but we have no easy way to know how people are using it,” said co-author Jennifer Mankoff, a professor at the university’s Paul G. Allen School of Computer Science & Engineering.

“Could we come up with a circuitless solution that could be printed on consumer-grade, off-the-shelf printers and allow the device itself to collect information? That's what we showed was possible.”

The printed devices use mechanical features to keep track of their use and a method called backscatter to share the information. Signals transmitted to the devices by an antenna are reflected back, sharing the information.

The team previously developed the first 3D-printed objects that connect to WiFi without electronics. The purely plastic devices measured levels in a cleaning liquid bottle and automatically ordered more when it ran out.

“Last time, we had a gear that turned in one direction. As liquid flowed through the gear, it would push a switch down to contact the antenna,” said lead author Vikram Iyer. “This time we have two antennas, one on top and one on bottom, that can be contacted by a switch attached to a gear. So opening a pill bottle cap moves the gear in one direction, which pushes the switch to contact one of the two antennas. And then closing the pill bottle cap turns the gear in the opposite direction, and the switch hits the other antenna.”

“The gear's teeth have a specific sequencing that encodes a message. It's like Morse code,” said co-author Justin Chan. “So when you turn the cap in one direction, you see the message going forward. But when you turn the cap in the other direction, you get a reverse message.”

The same method could monitor how people use prosthetic devices, the team said. They printed an e-Nable arm with a prototype of the bidirectional sensor to monitor the hand opening and closing by determining the angle of the wrist. A similar system could eventually provide data to help predict if people are going to abandon a device, Mankoff said.

The team also built an insulin pen that monitored its own use and signalled when it ran low. Each time the dispensing button was pressed, a spring compressed further. When a ratchet was released, the spring unwound and repeatedly set off the antenna, showing how many times the button had been pressed.

The next step will be taking the concepts and shrinking them into real products, Mankoff said.